Plant endophytic bacteria: A potential resource pool of electroactive micro-organisms.

AIMS: Electroactive micro-organisms play a significant role in microbial fuel cells. It is necessary to discover potential resources in plant endophytes. In this study, plant tissues were selected to isolate endophytic bacteria, and the electrochemical activity potential was evaluated. METHODS AND RESULTS: The microbial fuel cell (MFC) is used to evaluate the electricity-producing activity of endophytic bacteria in plant tissues, and the species distribution of micro-organisms in the anode of the MFC after inoculation of plant tissues is determined by high-throughput sequencing. Twenty-six strains of bacteria were isolated from plant tissues belonging to Angelica and Sweet Potato, of which 17 strains from six genera had electrochemical activity, including Bacillus sp., Pleomorphomonas sp., Rahnella sp., Shinella sp., Paenibacillus sp. and Staphylococcus sp. Moreover, the electricity-producing micro-organisms in the plant tissue are enriched. Pseudomonas and Clostridioides are the dominant genera of MFC anode inoculated with angelica tissue. Staphylococcus and Lachnoclostridium are the dominant genera in MFC anode inoculated with sweet potato tissue. And the most representative Gram-positive strain Staphylococcus succinus subsp. succinus H6 and plant tissue were further analysed for electrochemical activity. And a strain numbered H6 and plant tissue had a good electrogenerating activity. CONCLUSION: This study is of great significance for expanding the resource pool of electricity-producing micro-organisms and tapping the potential of plant endophytes for electricity-producing. SIGNIFICANCE AND IMPACT OF STUDY: This is the first study to apply plant endophytes to MFC to explore the characteristics of electricity production. It is of great significance for exploring the diversity of plant endophytes and the relationship between electricity producing bacteria and plants.

The inhibitory effect of volatile organic compounds produced by Bacillus subtilis CL2 on pathogenic fungi of wolfberry.

Bacillus subtilis strain CL2 is antagonistic to wolfberry postharvest pathogenic fungi. In this study, we isolated and screened this strain for in vitro experiments. The result of the two-sealed-base-plates method revealed that volatile organic compounds (VOCs) emitted from the strain CL2 inhibited the hyphal growth of four pathogenic fungi Mucor circinelloides LB1, Fusarium arcuatisporum LB5, Alternaria iridiaustralis LB7, and Colletotrichum fioriniae LB8. After exposure to VOCs for 5 days, the hyphal growth of the pathogen C. fioriniae LB8 was inhibited by 73%. Scanning electron microscopy revealed that the VOCs produced by B. subtilis CL2 caused the mycelium morphology of the pathogenic fungi to deform, twist, fold, and shrink. In the in vivo experiments, we noticed that VOCs could significantly reduce the weight loss rate of wolfberry fruits caused by the pathogenic fungus M. circinelloides LB1 and that the decay incidence rate were caused by the pathogenic fungi F. arcuatisporum LB5, A. iridiaustralis LB7, and C. fioriniae LB8. On the basis of the headspace-gas chromatography-ion mobility spectrometry analysis, seven VOCs produced by strain CL2 were identified. Among them, 2,3-butanedione and 3-methylbutyric acid are the main antifungal active substances. This study investigated the antifungal properties of VOCs produced by the strain CL2 on postharvest pathogenic fungi isolated from wolfberry fruits both in vivo and in vitro, thereby providing the theoretical basis for its future applications.

A potentially important resource: endophytic yeasts.

Recent advancements in the research on endophytes isolated from plants and crops have greatly broadened its application in various fields. Endophytic bacteria and endophytic fungi are known to promote the growth of various plants. Besides, the secondary metabolites such as alcohol and xylitol secreted by the endophytic yeast also help their hosts to resist microbial invasion. This makes them a potential substitute for chemical-based control methods. Moreover, the plant hosts can also provide nutrients for the growth of endophytic yeasts. To achieve the symbiotic relationship, yeasts must colonize most parts of the plant tissues, including intercellular spaces, cytoplasm, stomata of seeds, roots, stems, leaves, and fruits as well. Conventionally, isolation of endophytic yeasts from different plant tissues and understanding their interior plants colonization mechanism have remainedkey strategies to exploit their key potentials. In this review, we will elaborate on the diversity, characteristics of colonization, and the factors that influence the distribution of endophytic yeasts. This review also lays a theoretical foundation for the application of endophytic yeasts in various industrial and agricultural practices.